Release 10 of a Long Term Evolution (LTE for short) technology, that is, an R10 system can support a Carrier Aggregation (CA for short) technology, that is, multiple Component Carriers (CC for short) can be allocated to one user equipment (UE for short) to support a higher data transmission rate. A UE that supports CA may have one Primary Cell (PCell for short) and one or more Secondary Cells (SCell for short).
A future release of LTE, such as R12, may support LTE-Advanced Multi-Stream Aggregation (MSA for short). This is a new technology that is used to increase a cell edge rate and is proposed at a 3GPP LTE-Advanced future evolution conference. MSA may be applied to inter-base station coordination of a macro cell to increase an edge user rate, or may be applied in a heterogeneous networking scenario of a large cell and a small cell to increase a peak rate for a user and simplify mobility management, thereby creating consistent service experience for the user. In future development of mobile broadband, user experience is the biggest concern of operators. In a mobile communications coverage area, users in different geographical locations should enjoy a mobile service of same quality. However, in a cellular communications system, system performance at an inter-cell edge is often one of the biggest challenges during design of a mobile communications system. If LTE, a mainstream technology for future wireless communications, and an evolution technology of LTE cannot improve user experience at a cell edge location, wide application of LTE may face a great challenge. A core idea of MSA multi-stream aggregation is that with a dynamic system adjustment, a user can always receive downlink data from a cell or a cell group with a best signal and perform data stream aggregation. In a similar manner used in an uplink direction, the user always transmits uplink data to the cell or the cell group with the best signal and performs data stream aggregation on a network side.
For a UE that supports CA, MSA may be considered as cell aggregation of different base stations (Evolved NodeB, eNB for short). In a release earlier than R11, both a PCell and a Scell of a UE belong to a same eNB. However, for a UE in MSA, a PCell and a SCell may belong to different eNBs.
For a scenario in which a Macro eNB and a Pico eNB are in same coverage, a UE may receive both a signal from the Macro eNB and a signal from the Pico eNB. The Macro eNB implements a control plane function of the UE, including a mobility management function of the UE. The Pico eNB is mainly used to carry an indoor data service with low mobility, to implement a user plane function. That is, a user plane and a control plane of an air interface are in a separated manner, that is, C/U separation. A link from the Pico eNB to the UE is only responsible for data transmission on the user plane, and control plane signaling from the Pico eNB to the UE is transmitted over a link from the Macro eNB to the UE. A connection between the Pico eNB and the Macro eNB is a wired connection and is similar to an X2 interface. Once the UE and the Macro eNB establish an RRC connection, the Macro eNB transmits RRC configuration information required by the Pico eNB to the Pico eNB by using a newly-defined interface message. Related configuration information may be sent to the Pico eNB when the UE and the Macro eNB establish the RRC connection.
C/U separation may also be separation in broad sense. Referring to FIG. 1, FIG. 1 is a protocol stack architecture in the prior art. A Pico eNB establishes, for a signaling radio bearer (SRB for short), a protocol entity from a physical (Phy) layer to a Packet Data Convergence Protocol (PDCP) layer. Two sets of SRBs are established on a UE side and are respectively corresponding to a Macro eNB and the Pico eNB. In this protocol architecture, the Macro eNB may directly send generated RRC signaling to the UE, as shown by a dashed line A in FIG. 1; the Pico eNB may also transport RRC signaling to the UE, but the RRC signaling is generated by the Macro eNB, as shown by a dashed line B in FIG. 1.
Referring to FIG. 2, FIG. 2 is another protocol stack architecture in the prior art. A Pico eNB establishes, for an SRB, a protocol entity from Phy to RRC, but the Pico eNB is only responsible for configuration at bottom layers, that is, configuration of Phy, MAC, and RLC of the Pico eNB is completed by RRC of the Pico eNB. Two sets of SRBs are established on a UE side and are respectively corresponding to a Macro eNB and the Pico eNB. In this protocol architecture, the Macro eNB may send generated RRC signaling to the UE, and the Pico eNB may also generate RRC signaling and send the RRC signaling to the UE.
During a process of studying and practicing this method, the inventor of the present disclosure finds that, to support MSA, two sets of SRBs need to be established on the user equipment side to support RRC signaling from the Macro eNB and that from the Pico eNB, thereby increasing design complexity and costs.